1. Field of the Invention
The present invention relates to a method of applying miniaturized high-temperature free-grid strain gauges, more particularly those which are constructed of foil, and similarly constructed temperature measuring probes.
2. Discussion of the Prior Art
Presently known strain gauges have heretofore been limited to maximum temperatures of approximately 250.degree. C. during static or long term endurance tests, and to approximately 290.degree. C. and individually on occasion up to 400.degree. C., during relatively brief or short term dynamic measurements. Hereby, various resin systems serve as adhesives, whose limiting temperatures lie within similar ranges.
For effecting measurements in the temperature range in excess of 300.degree. C., utilization is made of free-grid strain gauges, i.e. of wire construction, which are cemented on through the intermediary of special ceramic adhesives, or are applied by a method which is related to plasma-jet spraying. For this purpose, the free-grid strain gauge must be located on an auxiliary or temporary backing having perforations or exposed locations, or a so-called masking. In order to fasten the strain gauge onto the test location, two operative steps are required, namely, (a) cementing or plasma-jet spraying the strain gauge grid elements through the perforations or exposed locations of the masking, and (b) stripping off of the masking and affixing the heretofore masked locations.
This described method for the second operative step generally works well for the normal size of grid but already poses considerable problems with regard to the smallest currently available high-temperature strain gauges which are of wire construction having a grid size of 3.2 .times. 1.6 mm. The connecting webs produced by the first operative step are, namely, so narrow (0.5 mm and less) that adhesibility to the base surface is not always adequate to again allow for stripping of the masking without injury to or deformation of the strain gauge grid during this sequence. Moreover, the high-temperature strain gauges have only a limited shelf life in view of the adhesive employed for the masking.
Additionally known in the art are free-grid strain gauges constituted of foil construction and having a miniaturized grid size of 0.8 .times. 0.8 mm. The actual measuring probe, comprising an etched foil formed of a chrome-nickel alloy, is supported on a continuous backing foil of plastic material foil of modified teflon, polyamide or a similar material. However, these types of foil constructed free-grid strain gauges cannot be processed by means of previously known methods for measuring applications at temperatures essentially in excess of 300.degree. C.